#!/bin/perl
# filename：test.pl
use strict; 
use warnings; 

#随便找一个比较好识别的序列 
my $DNA="AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\n"; 
my $i; 
my $mutant; 
srand(time|$$); 
$mutant=mutate($DNA); 
print "Mutate \n". $DNA; 
print "Here is the original DNA:\n"; 
print "$DNA\n"; 
print "Here is the mutant DNA:\n\n"; 
print "$mutant\n"; 
print "Here are 10 more successive mutations:\n"; 
for ($i=0;$i<10;++$i) 
{ 
   $mutant=mutate($mutant); 
   print "$mutant\n"; 
} 

#子程序：根据序列的长度定义一个随机位置的子程序 
sub randomposition 
{ 
   my($string)=@_; 
   return int(rand(length($string))); 
}
#子程序：从一个数组中随机选取一个元素 
sub randelement 
{ 
  my(@array)=@_; 
  return $array[rand @array]; 
} 

#子程序：引用上面的子程序，从ATGC四个碱基中随机选取一个 
sub randomnucleotide 
{ 
  my (@nucleotides)=qw/A T G C/; 
  return randelement(@nucleotides); 
} 

#子程序：生成突变的子程序 
sub mutate 
{ 
   my($dna)=@_; 
   my(@nucleotides)=qw(A T G C); 
   my($position)=randomposition($dna); 
   my($newbase)=randomnucleotide(@nucleotides); 
   substr($dna,$position,1,$newbase);#substr($string,$initial_position,$length,replacement substring) 
   return $dna; 
}